From a viewpoint of preventing global warming or saving energy, an idling stop system (also referred to as an economy-running system or an engine automatic stop-and-start system) in which an engine is automatically stopped when a vehicle stops on a red light at an intersection or the like and is restarted in response to an operation by a driver to start running again (an operation such as pressing down an accelerator pedal or stopping pressing a brake pedal) has been put into practical use.
In the vehicle incorporating such an idling stop system, when a predetermined condition for stopping is satisfied, the vehicle is controlled to stop the engine. In order to improve start-up property at the time of restart, a technique to stop the engine at a desired crank angle has been available. For example, Japanese Patent Laying-Open No. 2001-173473 discloses a control device of an internal combustion engine achieving improvement in start-up property of an engine by stopping the same at a desired crank angle. When it is determined that the condition for stopping the engine is satisfied, the control device of an internal combustion engine raises a manifold pressure and thereafter stops the engine.
According to the control device of the internal combustion engine disclosed in the above-mentioned publication, the manifold pressure is raised before the engine is stopped, so that a pressure in a combustion chamber of the engine is raised. Receiving such a pressure, a piston does not go beyond a compression top dead center, and the crank angle of the piston can be stopped at a desired angle (approximately BTDC 60° CA) before the TDC (Top Dead Center). Consequently, a cylinder before reaching the compression top dead center is ignited at the time of restart, whereby the start-up property of the engine is improved.
It is also possible to quickly restart the engine in a manner different from the publication described above. Specifically, when the engine of the vehicle incorporating the idling stop system is stopped, a fuel is injected in advance into a cylinder in an expansion stroke, and thereafter the engine is stopped. Then, the cylinder in the expansion stroke is ignited at next ignition and start.
In particular in a port injection type engine, in order to inject the fuel in advance into the cylinder in the expansion stroke, it is necessary to inject the fuel while the cylinder is in an intake stroke preceding the expansion stroke, and to stop the cylinder to be ignited at the time of restart when it enters the expansion stroke. On the other hand, if the fuel is injected in advance in the intake stroke, a pressure of an air-fuel mixture is raised in the compression stroke, and autoignition is likely. If autoignition occurs, torque is generated, which results in difficulty in controlling the piston or a crankshaft to stop at a desired position. In addition, if autoignition occurs, desired torque cannot be obtained even if the cylinder in the expansion stroke is ignited at the time of restart. That is, the start-up property of the engine is deteriorated.
Moreover, as in the control device of the internal combustion engine disclosed in the publication mentioned above, a stop position of the crankshaft cannot accurately be controlled with a throttle and an intake/exhaust valve alone, which results in deterioration of the start-up property. Furthermore, if the manifold pressure is increased as in the control device of the internal combustion engine disclosed in the publication mentioned above, magnitude of torque fluctuation becomes great, which leads to generation of vibration when the engine is stopped. As described above, when the stop position is controlled by raising the manifold pressure, the stop position cannot be controlled with high accuracy, and vibration is generated.